Pannoniasaurus
Pannoniasaurus is an extinct genus of tethysaurine mosasauroid known from the Late Cretaceous Csehbánya Formation (Santonian stage) of Hungary. It contains a single species, Pannoniasaurus inexpectatus,1 dubbed "unexpected" because it was discovered in freshwater sediments, unlike other mosasaurs, which were marine predators. It was a medium-sized mosasaur, reaching up to 6 m (20 ft) in length. Discovery and naming The holotype (MTM 2011.43.1) and referred specimens have been collected from the alluvial sediments of the Csehbánya Formation from various exposures at the Iharkút open-pit bauxite mine, Bakony Hills, Western Hungary since the discovery of the locality in 2000. A single vertebra has been collected in 1999 from the Ajka Coal Formation at the waste dump of the coal mines next to the town of Ajka, 20 km from Iharkút. Currently more than one hundred bones of Pannoniasaurus, sourced from a large number of individuals of differing age classes, are known from the alluvial flood-plain deposits that comprise the Csehbánya Formation. All specimens of Pannoniasaurus are currently housed in the Hungarian Natural History Museum, Budapest, Hungary. Description Pannoniasaurus was a medium-sized mosasauroid, estimated to grow up to a maximum of 6 metres (20 feet) in length. It exhibited a combination of primitive characteristics, such as having no predental rostrum, the premaxilla-maxilla suture ends anterior to or level with the midline of the fourth maxillary tooth, a nearly straight frontoparietal suture, and a shallow quadrate alar concavity. It also had elongated stapedial pit that was at least three times longer than it was wide. Tethysaurus is the type genus, as it is the best-represented genus of the subfamily, known from multiple partial skeletons. Thus the subfamily name derives from the name of its type genus. Pannoniasaurus is known from various material, including 2 isolated premaxillae, 3 maxillae, 2 postorbitofrontals, 2 quadrates, 3 dentaries, 3 splenials, 3 angulars, a coronoid, 2 surangulars, an articular, 91 isolated teeth, 20 cervical, 40 dorsal, 4 sacral, and 18 caudal vertebrae, 34 vertebral fragments, 3 ribs, 2 humeral fragments, and 4 ilia. Since all remains are isolated bones, the basis for the referral of this material to Pannoniasaurus is based on similar methods used by other authors, such as Houssaye et al. in their study of Pachyvaranus crassispondylus in 2011.2 The paratypes are known by MTM V.01.115, a left quadrate, and MTM 2007.31.1, a fragmentary left quadrate.1 Though all remains (including the holotype) of Pannoniasaurus are isolated bones, the density of the specimens, the various size classes, the large number of similar elements from individual animals, and their unique characters, make it possible to link them together into a single taxon.1 The preserved part of the maxilla bears 12 tooth sockets but the original maxillary tooth count might have been much higher. A number of isolated teeth were attributed to Pannoniasaurus that are similar to Halisaurus, being conical and curved posterolingually, bear crowns with fine anastomosing longitudinal striae, and have a strong mesial but weaker labiodistal carina.1 A single vertebra of Pannoniasaurus (MTM V.2000.21), as well as a variety of fish and crocodile teeth, were collected from the waste dump of the subterranean Ajka coal mine. The Ajka Coal Formation interdigitates with the Csehbánya Formation, the depositional environment of the latter was a floodplain, while the Ajka Coal Formation was formed in the accumulation basin of the same river system. Both of these facies were formed in the same paleogeographic area, which itself might have been part of a larger, but isolated landmass. Classification Category:Prehistoric reptiles of Europe Category:Mosasaurs